In the conventional electric glass melting process utilizing a vertically oriented melting chamber formed of conventional refractory materials, the glass batch is fed continuously at the top level of the melting chamber and molten glass is withdrawn also continuously at the bottom level of the chamber generally after the molten glass has been refined. Batch feeding means supply the glass batch to form a blanket extending partially or completely over the entire cross sectional area of the melting chamber which floats on the top of the molten glass in the chamber. This floating layer of batch blanket consists of powdered materials which exhibit a sufficiently low thermal conductivity to function as an insulator with respect to the electrical heating energy being supplied to the furnace electrodes. Various type electrode arrangements to supply the heating energy for melting the glass batch are known and generally include sets of individual electrodes which project into the melting chamber through the refractory sidewalls and are disposed at different elevations in the molten glass zone. It is known to locate one set of heating electrodes at the upper level of the molten glass zone and to further include at least one set of electrodes located therebelow in the molten glass having separate control means for applying electrical energy to each set of electrodes.
For high thermal efficiency in the above type glass melting process, it is desirable to maintain the batch blanket as thick as possible. However, the gaseous products which evolve from the glass batch must escape upwardly through the batch blanket if the glass batch is to be melted continuously in an uninterrupted manner. More particularly, if the gaseous products are trapped within or beneath the glass batch blanket, a phenomena wherein only partial melting of powdered materials occurs which can interrupt or terminate the continuous glass melting process. When these gaseous products cannot escape, a layer of foamy glass is formed within the batch blanket that can be sufficient to cause sudden lifting of the entire batch blanket as much as six inches in as short a time period as 15 minutes. The undesired layer of foamy glass itself forms an insulation preventing heat from the underlying electrodes to melt the batch blanket and can further undesirably elevate the temperature of the molten glass. The molten glass level can also drop when this phenomena takes place. Such accompanying effect cannot only disrupt the continuous glass melting operation but further produce undesired variations while the molten glass is still being withdrawn from the melting chamber. Certain means are already known to help avoid interruption of the continuous glass melting process due to entrapment of gas products from the glass batch, but the known means either sacrifice operating efficiency or have not proven entirely reliable. One method proposed to solve the problems encountered with gas entrapment in this manner utilizes physical dimensions and operating conditions in the melting chamber so that a batch blanket less than approximately six inches in thickness is maintained but such operation results in excessive heat loss and reduced thermal efficiency. The melting chamber has also been modified to include an overhanging tuckstone arrangement being located at the level where the batch blanket is deposited in an attempt to maintain a ring of molten glass through which the gases can escape. Although such arrangement permits maintenance of a batch blanket having 8-16 inches thickness, it has been found sensitive to changes in power input or batch charging rates sufficient to cause the undesired bridging condition above explained. Still different means to alleviate the general problem employs a rotating mechanical device to preserve an opening in the batch blanket for gas escape but this means introduces further complexity in the glass melting process and is also subject to the same undesirable bridging condition.